Time in Visa Limbo continues to be well used. I need to get to grips with IRT, big time. A good starting point is Baker's Basic Item Response Theory, and the software that goes with it, (you'll need Visual Basic 5.0 if you're running anything later than Windows 95, and I have no idea how to run it on a Mac or Linux or wtf).
There are a lot of web resources on IRT and Rasch measurement, and I'll link to them in a new post when I'm a bit further down the road with this.
I'm going to use the label IRT for posts connected with this, eschewing other terms such as CAT.